Automatic stopping device for plane lapping machine



Nov. 7, 1967' 55m |$O ET AL AUTOMATIC STOPPING DEVICE FOR PLANE LAPPING MACHINE Filed June 11, 1964 SCILLATOR FIG. I

FREQUENCY/ DISCRIMINATOR INVENTORS SEIJI KISO NAOTO NAKAMURA United States Patent AUTOMATIC STOPPING DEVICE FOR PLANE LAPPING MACHINE Seiji Kiso, Tokyo, and Naoto N akamura, Yokohama,

Japan, assignors to Kabushiiri-Kaisha Nihon Seikosho, Tokyo, Japan Filed June 11, 1964, Ser. No. 374,494 Claims priority, application Japan, June 20, 1963, 38/ 46,184 1 Claim. (Cl. 51-165) This invention relates to a device for automatically stopping an operation of a plane lapping machine at the instant a workpiece has been lapped to a predetermined dimension.

Heretofore, a dimension of any lapped workpiece could be measured only after the associated plane lapping machine was stopped to be operated whereupon a surface table was raised to remove the lapped workpiece from the machine followed by cleaning away of a lapping agent involved. It is desirable to measure a dimension of a workpiece being lapped during the operation of the machine, because there is no necessity of stopping the machine whenever the workpiece is desired to be measured in dimension. This results in an increase in operational efficiency. Also it is very desirable to stop the operation of the machine at the instant a workpiece worked by the machine has its dimension having reached a predetermined magnitude. This leads to the elimination of any artificial error in working and the facilitation of working operation.

An object of the invent-ion is, therefore, to provide a new and improved device for automatically stopping an operation of a plane lapping machine at the instant a workpiece being worked by the machine has its dimension reach a predetermined magnitude.

With this object in view, the invention resides in a device for automatically stopping an operation of a plane lapping machine including an upper surface plate and a lower surface plate between which a workpiece is lapped, said device including a probe element rigidly secured to the upper surface plate, detector coil means adjustably supported on a machine frame to be disposed directly below said probe element, means for controlling the height of said detector coil means relative to the lower surface plate, and electrical means operatively coupled to said detector coil means to produce a control signal as a function of a distance between said detector coil means and said probe element, said electrical means including control means responsive to said control signal to stop the operation of the machine.

The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings wherein FIGURE 1 is an elevational view, partly in section, of a plane lapping machine embodying the teachings of the invention; and

FIGURE 2 is a diagram of the apparatus of FIG. 1.

Referring now to the drawings there is illustrated a plane lapping machine including a machine frame 1 and a lower surface plate 2 rigidly secured on the machine frame 1. Disposed onto the lower surface plate 2 is a workpiece 3 which, in turn, is sandwiched between the lower surface plate 2 and an upper surface plate 4 under a suitable pressure by having a pressure applied downwardly thereto by the upper surface plate. The workpiece 3 is adapted to slide between the lower and upper surface plates 2 and 4 respectively as a carrier 5 moves.

A supporting arm 6 is suit-ably fixed on the upper surface plate 4 at a position where the arm does not interfere with the working operation and includes a probe element 7 of any suitable nonmagnetic material rigidly secured thereto at its free end.

The machine frame 1 is provided on one side with a 3,350,817 Patented Nov. 7, 1967 stand 8 substantially vertically supported th r and slightly spaced away from that side. The stand 8 is provided at the upper end with a vertical shaft 10 having a screw-threaded lower portion 9 screwed into the upper end of the same and having a flange 11 secured at the upper end. A support block 12 is fitted onto the vertical shaft 10 for movement along the shaft. Disposed between the flange 11 and the support block 12 is a compression spring 13 serving to press the support block 12 against a nut 14 screwed onto the screw-threaded portion 9 of the vertical shaft 10. The nut 14 is provided with graduations 15 for indicating its angular position relative to the shaft 10.

The support block 12 includes a radial support arm 16 extending below the support arm 6 and including a detector coil 17 rigidly secured at its free end at its position where the same is disposed directly below the probe element 7.

With this arrangement, the nut 14 can be controlled in its vertical position relative to the vertical shaft 10 to change the level of support block 12 to thereby adjust the position of the detector coil 17 with respect to the probe element such that a small gap is properly maintained therebet'ween.

The detector coil 17 is shown as being coupled to electrical device generally designated by the reference numeral 18, through a coaxial cable 19. The electrical device 18 includes an oscillation circuit for producing an oscillation wave at a predetermined stable frequency and a frequency discriminator circuit connected to the output of the oscillation circuit. The detector coil 17 is suitably coupled in parallel to the oscillation coil of the oscillation circuit. This arrangement just described may be of a conventional type and its detail need not be illustrated. The output of the frequency discriminator circuit is connected to indicating meter 20 which, in turn, includes a limit contact 21 displaceable along the path of the indieating pointer. The limit contact is connected to a control relay (not shown) serving to interrupt the current flow from conductor 22 which is connected to a power supply, to conductor 23 which supplies the current for operation of the machine, so as to stop the operation of the machine.

In operation the workpiece 3 sandwiched between the lower and upper surface plates 2 and 4 slides between both surface plates while being subject to a suitable pressure. At the same time a lapping agent is injected on the surface to be lapped of the workpiece for lapping. As the lapping operation proceeds, the dimension of the workpieces becomes thinner whereby the upper surface plate 4 is lowered by a distance corresponding to a decrease in the dimension of the workpiece. Strictly speaking, however, that distance should be equal to the decrease in dimension of the workpiece plus an abrasion loss of the upper surface plate. The abrasion loss, however, is eX- tremely low as compared with that of the workpiece. The downward movement of the upper surface plate 4 decreases the gap between the probe element 7 and the detector coil 17. As previously described, the detector coil 17 is coupled in parallel relationship with the oscillation coil of the oscillation circuit. Due to a flow of eddy current within the nonmagnetic probe element 7 disposed above the detector coil 17, developed by a change in the gap between the probe element and the detector coil, a magnetic flux from the detector coil 17 is prevented from flowing through the probe element 7 with the result that its inductance and hence the oscillation frequency changes. This change in frequency is indicated on the meter 20 through the action of the frequency discriminator circuit.

It is recalled that the meter 20 includes the displaceable limit contact. Therefore, in order to preset the meter 20 for a dimension to which a workpiece is to be lapped,

the limit contact has been displaced in accordance with that dimension of the workpiece. Then when the pointer of the meter 20 indicates the said dimension and hence contacts the limit contact, the control relay connected to the contact is energized tov interrupt the power for the machine to thereby stop the same.

If a thick workpiece 3 is desired to be lapped, the distance between the upper and lower surface plates 4 and 2 may be too great to sense the dimension of the workpiece after having been lapped. Under these circumstances, the nut 14 can'be rotated to move the support block 12. to thereby maintain the gap to the proper magnitude.

The graduations 15 provided on the outer periphery of the nut 14 for indicating the movement relative to the vertical shaft 9 and the indication on the meter 19 in the electric device 18 can be used to determine the dimension of the lapped workpiece.

The invention has several advantages. For example, for the reason that there is not the necessity of determining a dimension of a lapped workpiece after the machine has been stopped and that when the dimension of the lapped workpiece has reached its predetermined magnitude the machine is automatically stopped, the lapping operation is very easily performed and the workpiece is completely prevented from being lapped to an erroneous dimension. Also, since the probe element is not required to contact the detector coil, detecting means are not required to be removed and re-mounted on the machine each time the workpiece engages the machine. Furthermore, even though the upper surface table might be changed in its vertical position in accordance with a dimension of a workpiece before lapped the detector coil is not necessary to be controlled in level in order to contact the probe element. This leads to vary facilitation of the lapping operation with high efficiency. Because of the adjustable distance between the detector coil and the probe element, the device of the invention is suitable for lapping workpieces whose dimensions are of wide variety.

While the invention has been described in conjunction with a preferred embodiment thereof it is to be understood that various changes in the detail of construction and the arrangement and combination of the part may be made without departing from the spirit and scope of the invention.

What we claim is:

A device for automatically stopping the operation of a plane lapping machine which has an upper surface plate and a lower surface plate between which a workpiece is lapped and driving means for driving the machine, said device including a probe element rigidly secured to said upper surface plate, detector coil means adjustably supported on a machine frame and disposed directly below said probe element and spaced from said probe element, means for controlling the height of said detector coil means relative to the lower surface plate, and, electrical means including an oscillation circuit operatively coupled to said detector coil. means to detect a separation of said probe element from said detector coil. means as a change in electrical quantity while said probe element remains spaced from said detector coil means, said circuit means including an electric meter including a pointer and an adjustable contact to indicate said change in electrical quantity, said electrical means including control means responsive to said control signal and coupled to the driving means to stop the operation of the machine when the control signal reaches a predetermined value.

References Cited UNITED STATES PATENTS 3,063,206 11/1962 Meyerhoff et al 5l165 X LESTER M. SWINGLE, Primary Examiner.

WILLIAM M. DYER, JR., Examiner. 

